Altered Machinery of Protein Synthesis in Alzheimer's: From the Nucleolus to the Ribosome

Meta-Analysis of Transcriptomic Studies of Blood and Six Brain Regions Identifies a Consensus of 15 Cross-Tissue Mechanisms in Alzheimer's Disease and Suggests an Origin of Cross-Study Heterogeneity

The comprehensive genome-wide nature of transcriptome studies in Alzheimer's disease (AD) should provide a reliable description of disease molecular states. However, the genes and molecular systems nominated by transcriptomic studies do not always overlap. Even when results do align, it is not clear if those observations represent true consensus across many studies. A couple of sources of variation have been proposed to explain this variability, including tissue-of-origin and cohort type, but its basis remains uncertain. To address this variability and extract reliable results, we utilized all publicly available blood or brain transcriptomic datasets of AD, comprised of 24 brain studies with 4007 samples from six different brain regions, and eight blood studies with 1566 samples. We identified a consensus of AD-associated genes across brain regions and AD-associated gene-sets across blood and brain, generalizable machine learning and linear scoring classifiers, and significant contributors to biological diversity in AD datasets. While AD-associated genes did not significantly overlap between blood and brain, our findings highlighted 15 dysregulated processes shared across blood and brain in AD. The top five most significantly dysregulated processes were DNA replication, metabolism of proteins, protein localization, cell cycle, and programmed cell death. Conversely, addressing the discord across studies, we found that large-scale gene co-regulation patterns can account for a significant fraction of variability in AD datasets. Overall, this study ranked and characterized a compilation of genes and molecular systems consistently identified across a large assembly of AD transcriptome studies in blood and brain, providing potential candidate biomarkers and therapeutic targets.

Targeted downregulation of insulin signaling restricts human tau pathogenesis by reinstating the aberrant heterochromatin loss and mTOR/4EBP/S6K pathway in Drosophila

Tauopathies are a group of neurodegenerative diseases characterized by the accumulation of paired helical filaments (PHFs)/or neurofibrillary tangles (NFTs) in neuronal/glial cells. Besides hyperphosphorylation of tau protein, aberrant heterochromatin loss and translation dysfunction have emerged as other important aspects contributing to the disease pathogenesis. We have recently reported that tissue-specific downregulation of insulin signaling or its growth-promoting downstream sub-branch effectively reinstates the tau-mediated overactivated insulin pathway, and restricts pathogenic tau hyperphosphorylation and aggregate formation. We next investigated if the downregulation of the insulin pathway or its growth-promoting downstream sub-branch makes any impact on tau-mediated aberrant heterochromatin loss and translation dysfunction. For the first time, we demonstrate that tissue-specific downregulation of insulin signaling or its growth-promoting branch effectively restricts the pathogenic tau-induced heterochromatin loss. We further report that expression of human tau in Drosophila causes induction of the mTOR/4EBP/S6K pathway and energy disbalance which gets effectively balanced upon downregulation of insulin signaling. Our findings establish an imperative role of insulin signaling in effectively mitigating various aspects of tau etiology in Drosophila ranging from hyperphosphorylation, chromatin relaxation, and translational upsurge. Our findings could be beneficial in establishing novel therapeutic options against tauopathies.

Decoding the molecular script of 2'-O-ribomethylation: Implications across CNS disorders

Emerging evidence underscores the critical role of impaired mRNA translation in various neurobiological conditions. Ribosomal RNA (rRNA), essential for protein synthesis, undergoes crucial post-transcriptional modifications such as 2'-O-ribose methylation, pseudouridylation, and base modifications. These modifications, particularly 2'-O-ribose methylation is vital for stabilizing rRNA structures and optimizing translation efficiency by regulating RNA integrity and its interactions with proteins. Concentrated in key regions like decoding sites and the peptidyl transferase center, dysregulation of these modifications can disrupt ribosomal function, contributing to the pathogenesis of diverse neurological conditions, including mental health disorders, developmental abnormalities, and neurodegenerative diseases. Mechanistically, 2'-O-ribose methylation involves interactions between small nucleolar RNAs (snoRNAs), snoRNPs, and fibrillarin, forming a complex regulatory network crucial for maintaining ribosomal integrity and function. Recent research highlights the association of defective ribosome biogenesis with a spectrum of CNS disorders, emphasizing the importance of understanding rRNA mechanisms in disease pathology. This review focuses on the pivotal role of 2'-O-ribose methylation in shaping ribosomal function and its potential implications for unraveling the pathophysiology of CNS disorders. Insights gained from studying these RNA modifications could pave the way for new therapeutic strategies targeting ribosomal dysfunction and associated neuropathological conditions, advancing precision medicine and therapeutic interventions.

Alzheimer's Disease: Exploring the Landscape of Cognitive Decline

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by cognitive decline, memory loss, and impaired daily functioning. The pathology of AD is marked by the accumulation of amyloid beta plaques and tau protein tangles in the brain, along with neuroinflammation and synaptic dysfunction. Genetic factors, such as mutations in APP, PSEN1, and PSEN2 genes, as well as the APOE ε4 allele, contribute to increased risk of acquiring AD. Currently available treatments provide symptomatic relief but do not halt disease progression. Research efforts are focused on developing disease-modifying therapies that target the underlying pathological mechanisms of AD. Advances in identification and validation of reliable biomarkers for AD hold great promise for enhancing early diagnosis, monitoring disease progression, and assessing treatment response in clinical practice in effort to alleviate the burden of this devastating disease. In this paper, we analyze data from the CAS Content Collection to summarize the research progress in Alzheimer's disease. We examine the publication landscape in effort to provide insights into current knowledge advances and developments. We also review the most discussed and emerging concepts and assess the strategies to combat the disease. We explore the genetic risk factors, pharmacological targets, and comorbid diseases. Finally, we inspect clinical applications of products against AD with their development pipelines and efforts for drug repurposing. The objective of this review is to provide a broad overview of the evolving landscape of current knowledge regarding AD, to outline challenges, and to evaluate growth opportunities to further efforts in combating the disease.

SERBP1 interacts with PARP1 and is present in PARylation-dependent protein complexes regulating splicing, cell division, and ribosome biogenesis

RNA binding proteins (RBPs) containing intrinsically disordered regions (IDRs) are present in diverse molecular complexes where they function as dynamic regulators. Their characteristics promote liquid-liquid phase separation (LLPS) and the formation of membraneless organelles such as stress granules and nucleoli. IDR-RBPs are particularly relevant in the nervous system and their dysfunction is associated with neurodegenerative diseases and brain tumor development. Serpine1 mRNA-binding protein 1 (SERBP1) is a unique member of this group, being mostly disordered and lacking canonical RNA-binding domains. We defined SERBP1's interactome, uncovered novel roles in splicing, cell division and ribosomal biogenesis, and showed its participation in pathological stress granules and Tau aggregates in Alzheimer's brains. SERBP1 preferentially interacts with other G-quadruplex (G4) binders, implicated in different stages of gene expression, suggesting that G4 binding is a critical component of SERBP1 function in different settings. Similarly, we identified important associations between SERBP1 and PARP1/polyADP-ribosylation (PARylation). SERBP1 interacts with PARP1 and its associated factors and influences PARylation. Moreover, protein complexes in which SERBP1 participates contain mostly PARylated proteins and PAR binders. Based on these results, we propose a feedback regulatory model in which SERBP1 influences PARP1 function and PARylation, while PARylation modulates SERBP1 functions and participation in regulatory complexes.

MAD-microbial (origin of) Alzheimer's disease hypothesis: from infection and the antimicrobial response to disruption of key copper-based systems

Microbes have been suspected to cause Alzheimer's disease since at least 1908, but this has generally remained unpopular in comparison to the amyloid hypothesis and the dominance of Aβ and Tau. However, evidence has been accumulating to suggest that these earlier theories are but a manifestation of a common cause that can trigger and interact with all the major molecular players recognized in AD. Aβ, Tau and ApoE, in particular appear to be molecules with normal homeostatic functions but also with alternative antimicrobial functions. Their alternative functions confer the non-immune specialized neuron with some innate intracellular defenses that appear to be re-appropriated from their normal functions in times of need. Indeed, signs of infection of the neurons by biofilm-forming microbial colonies, in synergy with herpes viruses, are evident from the clinical and preclinical studies we discuss. Furthermore, we attempt to provide a mechanistic understanding of the AD landscape by discussing the antimicrobial effect of Aβ, Tau and ApoE and Lactoferrin in AD, and a possible mechanistic link with deficiency of vital copper-based systems. In particular, we focus on mitochondrial oxidative respiration via complex 4 and ceruloplasmin for iron homeostasis, and how this is similar and possibly central to neurodegenerative diseases in general. In the case of AD, we provide evidence for the microbial Alzheimer's disease (MAD) theory, namely that AD could in fact be caused by a long-term microbial exposure or even long-term infection of the neurons themselves that results in a costly prolonged antimicrobial response that disrupts copper-based systems that govern neurotransmission, iron homeostasis and respiration. Finally, we discuss potential treatment modalities based on this holistic understanding of AD that incorporates the many separate and seemingly conflicting theories. If the MAD theory is correct, then the reduction of microbial exposure through use of broad antimicrobial and anti-inflammatory treatments could potentially alleviate AD although this requires further clinical investigation.

Pathogenic tau induces an adaptive elevation in mRNA translation rate at early stages of disease

Alterations in the rate and accuracy of messenger RNA (mRNA) translation are associated with aging and several neurodegenerative disorders, including Alzheimer's disease and related tauopathies. We previously reported that error-containing RNA that are normally cleared via nonsense-mediated mRNA decay (NMD), a key RNA surveillance mechanism, are translated in the adult brain of a Drosophila model of tauopathy. In the current study, we find that newly-synthesized peptides and translation machinery accumulate within nuclear envelope invaginations that occur as a consequence of tau pathology, and that the rate of mRNA translation is globally elevated in early stages of disease in adult brains of Drosophila models of tauopathy. Polysome profiling from adult heads of tau transgenic Drosophila reveals the preferential translation of specific mRNA that have been previously linked to neurodegeneration. Unexpectedly, we find that panneuronal elevation of NMD further elevates the global translation rate in tau transgenic Drosophila, as does treatment with rapamycin. As NMD activation and rapamycin both suppress tau-induced neurodegeneration, their shared effect on translation suggests that elevated rates of mRNA translation are an early adaptive mechanism to limit neurodegeneration. Our work provides compelling evidence that tau-induced deficits in NMD reshape the tau translatome by increasing translation of RNA that are normally repressed in healthy cells.

Distinct calcium sources regulate temporal profiles of NMDAR and mGluR-mediated protein synthesis

Calcium signaling is integral for neuronal activity and synaptic plasticity. We demonstrate that the calcium response generated by different sources modulates neuronal activity-mediated protein synthesis, another process essential for synaptic plasticity. Stimulation of NMDARs generates a protein synthesis response involving three phases-increased translation inhibition, followed by a decrease in translation inhibition, and increased translation activation. We show that these phases are linked to NMDAR-mediated calcium response. Calcium influx through NMDARs elicits increased translation inhibition, which is necessary for the successive phases. Calcium through L-VGCCs acts as a switch from translation inhibition to the activation phase. NMDAR-mediated translation activation requires the contribution of L-VGCCs, RyRs, and SOCE. Furthermore, we show that IP3-mediated calcium release and SOCE are essential for mGluR-mediated translation up-regulation. Finally, we signify the relevance of our findings in the context of Alzheimer's disease. Using neurons derived from human fAD iPSCs and transgenic AD mice, we demonstrate the dysregulation of NMDAR-mediated calcium and translation response. Our study highlights the complex interplay between calcium signaling and protein synthesis, and its implications in neurodegeneration.

DNA Damage and Chromatin Rearrangement Work Together to Promote Neurodegeneration

Neurodegenerative diseases have a complex origin and are composed of genetic and environmental factors. Both DNA damage and chromatin rearrangement are important processes that occur under pathological conditions and in neurons functioning properly. While numerous studies have demonstrated the inseparable relationship between DNA damage and chromatin organization, understanding of this relationship, especially in neurodegenerative diseases, requires further study. Interestingly, recent studies revealed that known hallmark proteins involved in neurodegenerative diseases function in both DNA damage and chromatin reorganization, and this review discusses the current knowledge of this relationship. This review focused on hallmark proteins involved in various neurodegenerative diseases, such as the microtubule-associated protein tau, TAR DNA/RNA binding protein 43 (TDP-43), superoxide dismutase 1 (SOD1), fused in sarcoma (FUS), huntingtin (HTT), α-synuclein, and β-amyloid precursor protein (APP). Hence, DNA damage and chromatin rearrangement are associated with disease mechanisms in distinct neurodegenerative diseases. Targeting common modulators of DNA repair and chromatin reorganization may lead to promising therapies for treating neurodegeneration.

Subcellular proteomics insights into Alzheimer's disease development

Alzheimer's disease (AD), one of the most common dementias, is a neurodegenerative disease characterized by cognitive impairment and decreased judgment function. The expected number of AD patient is increasing in the context of the world's advancing medical care and increasing human life expectancy. Since current molecular mechanism studies on AD pathogenesis are incomplete, there is no specific and effective therapeutic agent. Mass spectrometry (MS)-based unbiased proteomics studies provide an effective and comprehensive approach. Many advances have been made in the study of the mechanism, diagnostic markers, and drug targets of AD using proteomics. This paper focus on subcellular level studies, reviews studies using proteomics to study AD-associated mitochondrial dysfunction, synaptic, and myelin damage, the protein composition of amyloid plaques (APs) and neurofibrillary tangles (NFTs), changes in tissue extracellular vehicles (EVs) and exosome proteome, and the protein changes in ribosomes and lysosomes. The methods of sample separation and preparation and proteomic analysis as well as the main findings of these studies are involved. The results of these proteomics studies provide insights into the pathogenesis of AD and provide theoretical resource and direction for future research in AD, helping to identify new biomarkers and drugs targets for AD.

Silencing Apoe with divalent-siRNAs improves amyloid burden and activates immune response pathways in Alzheimer's disease

INTRODUCTION

The most significant genetic risk factor for late-onset Alzheimer's disease (AD) is APOE4, with evidence for gain- and loss-of-function mechanisms. A clinical need remains for therapeutically relevant tools that potently modulate APOE expression.

METHODS

We optimized small interfering RNAs (di-siRNA, GalNAc) to potently silence brain or liver Apoe and evaluated the impact of each pool of Apoe on pathology.

RESULTS

In adult 5xFAD mice, siRNAs targeting CNS Apoe efficiently silenced Apoe expression and reduced amyloid burden without affecting systemic cholesterol, confirming that potent silencing of brain Apoe is sufficient to slow disease progression. Mechanistically, silencing Apoe reduced APOE-rich amyloid cores and activated immune system responses.

DISCUSSION

These results establish siRNA-based modulation of Apoe as a viable therapeutic approach, highlight immune activation as a key pathway affected by Apoe modulation, and provide the technology to further evaluate the impact of APOE silencing on neurodegeneration.

Phosphorylation regulates tau's phase separation behavior and interactions with chromatin

Tau is a microtubule-associated protein often found in neurofibrillary tangles (NFTs) in the brains of patients with Alzheimer's disease. Beyond this context, mounting evidence suggests that tau localizes into the nucleus, where it may play a role in DNA protection and heterochromatin regulation. The molecular mechanisms behind these observations are currently unclear. Using in vitro biophysical experiments, here we demonstrate that tau can undergo liquid-liquid phase separation (LLPS) with DNA, mononucleosomes, and reconstituted nucleosome arrays under low salt conditions. Low concentrations of tau promote chromatin compaction and protect DNA from digestion. While the material state of samples at physiological salt is dominated by chromatin oligomerization, tau can still associate strongly and reversibly with nucleosome arrays. These properties are driven by tau's strong interactions with linker and nucleosomal DNA. In addition, tau co-localizes into droplets formed by nucleosome arrays and phosphorylated HP1α, a key heterochromatin constituent thought to function through an LLPS mechanism. Importantly, LLPS and chromatin interactions are disrupted by aberrant tau hyperphosphorylation. These biophysical properties suggest that tau may directly impact DNA and chromatin accessibility and that loss of these interactions could contribute to the aberrant nuclear effects seen in tau pathology.

Exhaustive exercise decreases tau phosphorylation and modifies biological processes associated with the protein translation and electron transport chain in P301L tau transgenic mice

Stress response is a fundamental mechanism for cell survival, providing protection under unfavorable conditions. Mitochondrial stress, in particular, can trigger mitophagy, a process that restores cellular health. Exhaustive exercise (EE) is a form of acute mitochondrial stress. The objective of this current study is to investigate the impact of EE on tau pathology in pR5 mice, as well as the potential underlying mechanisms. To evaluate this, we examined the levels of total and phosphorylated tau in the hippocampus of pR5 mice, both with and without EE treatment. Furthermore, the application of weighted correlation network analysis (WGCNA) was employed to identify protein modules associated with the phenotype following the proteomic experiment. The findings of our study demonstrated a significant decrease in tau phosphorylation levels upon EE treatment, in comparison to the pR5 group. Moreover, the proteomic analysis provided additional insights, revealing that the mitigation of tau pathology was primarily attributed to the modulation of various pathways, such as translation factors and oxidative phosphorylation. Additionally, the analysis of heatmaps revealed a significant impact of EE treatment on the translation process and electron transport chain in pR5 mice. Furthermore, biochemical analysis provided further confirmation that EE treatment effectively modulated the ATP level in pR5 mice. In conclusion, our study suggests that the observed decrease in tau phosphorylation resulting from EE treatment may primarily be attributed to its regulation of the translation process and enhancement of mitochondrial function.

Proteomic Analysis of a Rat Streptozotocin Model Shows Dysregulated Biological Pathways Implicated in Alzheimer's Disease

Alzheimer's Disease (AD) is an age-related neurodegenerative disorder characterized by progressive memory loss and cognitive impairment, affecting 35 million individuals worldwide. Intracerebroventricular (ICV) injection of low to moderate doses of streptozotocin (STZ) in adult male Wistar rats can reproduce classical physiopathological hallmarks of AD. This biological model is known as ICV-STZ. Most studies are focused on the description of behavioral and morphological aspects of the ICV-STZ model. However, knowledge regarding the molecular aspects of the ICV-STZ model is still incipient. Therefore, this work is a first attempt to provide a wide proteome description of the ICV-STZ model based on mass spectrometry (MS). To achieve that, samples from the pre-frontal cortex (PFC) and hippocampus (HPC) of the ICV-STZ model and control (wild-type) were used. Differential protein abundance, pathway, and network analysis were performed based on the protein identification and quantification of the samples. Our analysis revealed dysregulated biological pathways implicated in the early stages of late-onset Alzheimer's disease (LOAD), based on differentially abundant proteins (DAPs). Some of these DAPs had their mRNA expression further investigated through qRT-PCR. Our results shed light on the AD onset and demonstrate the ICV-STZ as a valid model for LOAD proteome description.

An Overview of UBTF Neuroregression Syndrome

Recently, a recurrent de novo dominant mutation in UBTF (c.628G>A, p.Glu210Lys; UBTF E210K) was identified as the cause of a neurological disorder which has been named UBTF Neuroregression Syndrome (UNS), or Childhood-Onset Neurodegeneration with Brain Atrophy (CONDBA). To date, only 17 cases have been reported worldwide. The molecular etiology is a pathogenic variant, E210K, within the HMG-box 2 of Upstream Binding Transcription Factor (UBTF). UBTF, a nucleolar protein, plays an important role in ribosomal RNA (rRNA) synthesis, nucleolar integrity, and cell survival. This variant causes unstable preinitiation complexes to form, resulting in altered rDNA chromatin structures, rRNA dysregulation, DNA damage, and ultimately, neurodegeneration. Defining clinical characteristics of the disorder include but are not limited to developmental regression beginning at approximately three years of age, progressive motor dysfunction, declining cognition, ambulatory loss, and behavioral problems. Histological and neuroimaging abnormalities include cortical atrophy, white matter deficits, and enlarged ventricles. Herein, we present a detailed overview of all published cases as well as the functional roles of UBTF to better understand the pathophysiology. Bringing undiagnosed cases to the attention of clinicians and researchers by making them aware of the clinical features will improve research and support the development of therapeutic interventions.

Trazodone rescues dysregulated synaptic and mitochondrial nascent proteomes in prion neurodegeneration

The unfolded protein response (UPR) is rapidly gaining momentum as a therapeutic target for protein misfolding neurodegenerative diseases, in which its overactivation results in sustained translational repression leading to synapse loss and neurodegeneration. In mouse models of these disorders, from Alzheimer's to prion disease, modulation of the pathway-including by the licensed drug, trazodone-restores global protein synthesis rates with profound neuroprotective effects. However, the precise nature of the translational impairment, in particular the specific proteins affected in disease, and their response to therapeutic UPR modulation are poorly understood. We used non-canonical amino acid tagging (NCAT) to measure de novo protein synthesis in the brains of prion-diseased mice with and without trazodone treatment, in both whole hippocampus and cell-specifically. During disease the predominant nascent proteome changes occur in synaptic, cytoskeletal and mitochondrial proteins in both hippocampal neurons and astrocytes. Remarkably, trazodone treatment for just 2 weeks largely restored the whole disease nascent proteome in the hippocampus to that of healthy, uninfected mice, predominantly with recovery of proteins involved in synaptic and mitochondrial function. In parallel, trazodone treatment restored the disease-associated decline in synapses and mitochondria and their function to wild-type levels. In conclusion, this study increases our understanding of how translational repression contributes to neurodegeneration through synaptic and mitochondrial toxicity via depletion of key proteins essential for their function. Further, it provides new insights into the neuroprotective mechanisms of trazodone through reversal of this toxicity, relevant for the treatment of neurodegenerative diseases via translational modulation.

Tau: More than a microtubule-binding protein in neurons

Tau protein was discovered as a microtubule-associated protein nearly 50 years ago, and our understanding of tau has revolved around that role. Even with tau's rise to stardom as a central player in neurodegenerative disease, therapeutic efforts have largely been targeted toward cytoskeletal changes. While some studies hinted toward non-cytoskeletal roles for tau, it is only fairly recently that these ideas have begun to receive considerable attention. Many new binding partners for tau have been identified, including DNA, RNA, RNA-binding proteins, some receptors, and other tau molecules. The diversity of tau binding partners coupled with the discovery of tau other than axonal compartments such as nucleus, dendrites, and synapses have led to the proposal of novel functions for tau in roles such as nuclear stability, cell signaling, transcriptional processing, and protein synthesis. Tau self-assembly in particular has made an impact, leading to the hypothesis that a prion-like function of hyperphosphorylated tau is central to tauopathies. With tau emerging as a multifaceted protein that operates in many parts of the cell and with many molecular partners, the field of tau biology is primed for discoveries that can provide new perspectives on both the unique biochemistry of tau and the nature of devastating neurological diseases.

Polyamine Dysregulation and Nucleolar Disruption in Alzheimer's Disease

A hypothesis of Alzheimer's disease etiology is proposed describing how cellular stress induces excessive polyamine synthesis and recycling which can disrupt nucleoli. Polyamines are essential in nucleolar functions, such as RNA folding and ribonucleoprotein assembly. Changes in the nucleolar pool of anionic RNA and cationic polyamines acting as counterions can cause significant nucleolar dynamics. Polyamine synthesis reduces S-adenosylmethionine which, at low levels, triggers tau phosphorylation. Also, polyamine recycling reduces acetyl-CoA needed for acetylcholine, which is low in Alzheimer's disease. Extraordinary nucleolar expansion and/or contraction can disrupt epigenetic control in peri-nucleolar chromatin, such as chromosome 14 with the presenilin-1 gene; chromosome 21 with the amyloid precursor protein gene; chromosome 17 with the tau gene; chromosome 19 with the APOE4 gene; and the inactive X chromosome (Xi; aka "nucleolar satellite") with normally silent spermine synthase (polyamine synthesis) and spermidine/spermine-N1-acetyltransferase (polyamine recycling) alleles. Chromosomes 17, 19 and the Xi have high concentrations of Alu elements which can be transcribed by RNA polymerase III if positioned nucleosomes are displaced from the Alu elements. A sudden flood of Alu RNA transcripts can competitively bind nucleolin which is usually bound to Alu sequences in structural RNAs that stabilize the nucleolar heterochromatic shell. This Alu competition leads to loss of nucleolar integrity with leaking of nucleolar polyamines that cause aggregation of phosphorylated tau. The hypothesis was developed with key word searches (e.g., PubMed) using relevant terms (e.g., Alzheimer's, lupus, nucleolin) based on a systems biology approach and exploring autoimmune disease tautology, gaining synergistic insights from other diseases.

A Continuous Extension of Gene Set Enrichment Analysis Using the Likelihood Ratio Test Statistics Identifies Vascular Endothelial Growth Factor as a Candidate Pathway for Alzheimer's Disease via ITGA5

BACKGROUND

Alzheimer's disease (AD) involves brain neuropathologies such as amyloid plaque and hyperphosphorylated tau tangles and is accompanied by cognitive decline. Identifying the biological mechanisms underlying disease onset and progression based on quantifiable phenotypes will help understand disease etiology and devise therapies.

OBJECTIVE

Our objective was to identify molecular pathways associated with hallmark AD biomarkers and cognitive status, accounting for variables such as age, sex, education, and APOE genotype.

METHODS

We introduce a pathway-based statistical approach, extending the gene set likelihood ratio test to continuous phenotypes. We first analyzed independently each of the three phenotypes (amyloid-β, tau, cognition) using continuous gene set likelihood ratio tests to account for covariates, including age, sex, education, and APOE genotype. The analysis involved 634 subjects with data available for all three phenotypes, allowing for the identification of common pathways.

RESULTS

We identified 14 pathways significantly associated with amyloid-β; 5 associated with tau; and 174 associated with cognition, which showed a larger number of pathways compared to biomarkers. A single pathway, vascular endothelial growth factor receptor binding (VEGF-RB), exhibited associations with all three phenotypes. Mediation analysis showed that among the VEGF-RB family genes, ITGA5 mediates the relationship between cognitive scores and pathological biomarkers.

CONCLUSIONS

We presented a new statistical approach linking continuous phenotypes, gene expression across pathways, and covariates like sex, age, and education. Our results reinforced VEGF RB2's role in AD cognition and demonstrated ITGA5's significant role in mediating the AD pathology-cognition connection.

Novel method for collecting hippocampal interstitial fluid extracellular vesicles (EVISF ) reveals sex-dependent changes in microglial EV proteome in response to Aβ pathology

Brain-derived extracellular vesicles (EVs) play an active role in Alzheimer's disease (AD), relaying important physiological information about their host tissues. The internal cargo of EVs is protected from degradation, making EVs attractive AD biomarkers. However, it is unclear how circulating EVs relate to EVs isolated from disease-vulnerable brain regions. We developed a novel method for collecting EVs from the hippocampal interstitial fluid (ISF) of live mice. EVs (EVISF ) were isolated via ultracentrifugation and characterized by nanoparticle tracking analysis, immunogold labelling, and flow cytometry. Mass spectrometry and proteomic analyses were performed on EVISF cargo. EVISF were 40-150 nm in size and expressed CD63, CD9, and CD81. Using a model of cerebral amyloidosis (e.g., APPswe, PSEN1dE9 mice), we found protein concentration increased but protein diversity decreased with Aβ deposition. Genotype, age, and Aβ deposition modulated proteostasis- and immunometabolic-related pathways. Changes in the microglial EVISF proteome were sexually dimorphic and associated with a differential response of plaque associated microglia. We found that female APP/PS1 mice have more amyloid plaques, less plaque associated microglia, and a less robust- and diverse- EVISF microglial proteome. Thus, in vivo microdialysis is a novel technique for collecting EVISF and offers a unique opportunity to explore the role of EVs in AD.

Phosphorylation regulates tau's phase separation behavior and interactions with chromatin

Tau is a microtubule-associated protein often found in neurofibrillary tangles (NFTs) in the brains of patients with Alzheimer's disease (AD). Beyond this context, mounting evidence suggests that tau localizes into the nucleus, where it may play a role in DNA protection and heterochromatin regulation. Models of tau depletion or pathology show loss of genetically silent heterochromatin, aberrant expression of heterochromatic genes, and transposable element activation. The molecular mechanisms behind these observations are currently unclear. Using in vitro biophysical experiments, here we demonstrate that tau can undergo liquid-liquid phase separation (LLPS) with DNA, mononucleosomes, and reconstituted nucleosome arrays under low salt conditions. Low concentrations of tau promote chromatin compaction and protect DNA from digestion. While the material state of samples at physiological salt is dominated by chromatin oligomerization, tau can still associate strongly and reversibly with nucleosome arrays. These properties are driven by tau's strong interactions with linker and nucleosomal DNA, while magic angle spinning (MAS) solid-state NMR experiments show that tau binding does not drastically alter nucleosome structure and dynamics. In addition, tau co-localizes into droplets formed by nucleosome arrays and phosphorylated HP1α, a key heterochromatin constituent thought to function through an LLPS mechanism. Importantly, LLPS and chromatin interactions are disrupted by aberrant tau hyperphosphorylation. These biophysical properties suggest that tau may directly impact DNA and chromatin accessibility and that loss of these interactions could contribute to the aberrant nuclear effects seen in tau pathology.

Nuclear face of Tau: an inside player in neurodegeneration

Tau (Tubulin associated unit) protein is a major hallmark of Alzheimer's disease (AD) and tauopathies. Tau is predominantly an axonal protein with a crucial role in the stabilization and dynamics of the microtubules. Since the discovery of Tau protein in 1975, research efforts were concentrated on the pathophysiological role of Tau protein in the context of the microtubules. Although, for more than three decades, different localizations of Tau protein have been discovered e.g., in the nuclear compartments. Discovery of the role of Tau protein in various cellular compartments especially in the nucleus opens up a new fold of complexity in tauopathies. Data from cellular models, animal models, and the human brain indicate that nuclear Tau is crucial for genome stability and to cope with cellular distress. Moreover, it's nature of nuclear translocation, its interactions with the nuclear DNA/RNA and proteins suggest it could play multiple roles in the nucleus. To comprehend Tau pathophysiology and efficient Tau-based therapies, there is an urgent need to understand whole repertoire of Tau species (nuclear and cytoplasmic) and their functional relevance. To complete the map of Tau repertoire, understanding of various species of Tau in the nucleus and cytoplasm, identification if specific transcripts of Tau, isoforms and post-translational modifications could foretell Tau's localizations and functions, and how they are modified in neurodegenerative diseases like AD, is urgently required. In this review, we explore the nuclear face of Tau protein, its nuclear localizations and functions and its linkage with Alzheimer's disease.

Music compensates for altered gene expression in age-related cognitive disorders

Extensive literature has explored the beneficial effects of music in age-related cognitive disorders (ACD), but limited knowledge exists regarding its impact on gene expression. We analyzed transcriptomes of ACD patients and healthy controls, pre-post a music session (n = 60), and main genes/pathways were compared to those dysregulated in mild cognitive impairment (MCI) and Alzheimer's disease (AD) as revealed by a multi-cohort study (n = 1269 MCI/AD and controls). Music was associated with 2.3 times more whole-genome gene expression, particularly on neurodegeneration-related genes, in ACD than in controls. Co-expressed gene-modules and pathways analysis demonstrated that music impacted autophagy, vesicle and endosome organization, biological processes commonly dysregulated in MCI/AD. Notably, the data indicated a strong negative correlation between musically-modified genes/pathways in ACD and those dysregulated in MCI/AD. These findings highlight the compensatory effect of music on genes/biological processes affected in MCI/AD, providing insights into the molecular mechanisms underlying the benefits of music on these disorders.

Simple model systems reveal conserved mechanisms of Alzheimer's disease and related tauopathies

The lack of effective therapies that slow the progression of Alzheimer's disease (AD) and related tauopathies highlights the need for a more comprehensive understanding of the fundamental cellular mechanisms underlying these diseases. Model organisms, including yeast, worms, and flies, provide simple systems with which to investigate the mechanisms of disease. The evolutionary conservation of cellular pathways regulating proteostasis and stress response in these organisms facilitates the study of genetic factors that contribute to, or protect against, neurodegeneration. Here, we review genetic modifiers of neurodegeneration and related cellular pathways identified in the budding yeast Saccharomyces cerevisiae, the nematode Caenorhabditis elegans, and the fruit fly Drosophila melanogaster, focusing on models of AD and related tauopathies. We further address the potential of simple model systems to better understand the fundamental mechanisms that lead to AD and other neurodegenerative disorders.

BANF1 promotes glutamate-induced apoptosis of HT-22 hippocampal neurons

BACKGROUND

Glutamate exposure was fatal to HT-22 neuronal cells that derived from mouse hippocampus. This is often used as a model for hippocampus neurodegeneration in vitro. The targets relevant to glutamate-induced neuronal toxicity is not fully understood. In this study, we aimed to identify crucial factors associated with glutamate-induced cytotoxicity in HT-22 cells.

METHODS

HT-22 cells were treated with 7.5 mM glutamate for 24 h and isobaric tags for relative and absolute quantitation (iTRAQ) proteomic analysis conducted to identify the differentially expressed proteins. Differential proteins were subjected to Gene Ontology analyses. Upregulation of barrier to autointegration factor (BANF1/BANF1) protein was confirmed by RT-qPCR and western blotting. Cell viability was measured by CKK-8 and MTT assays. Cell apoptosis rates and intracellular reactive oxygen species (ROS) levels were detected using flow cytometry.

RESULTS

A total of 5811 proteins were quantified by iTRAQ, 50 of which were recognized as significantly differential proteins (fold change ≥ 1.5 and P ≤ 0.05); 26 proteins were up-regulated and 24 were down-regulated after exposure to glutamate. GO enrichment analysis showed that the apoptotic signaling pathway was involved in cell death induced by glutamate. BANF1 expression level was markedly increased in HT-22 cells after glutamate treatment. Further, knockdown of BANF1 alleviated glutamate-mediated cell death with lower ROS levels.

CONCLUSIONS

In conclusion, we successfully filtered out differential proteins relevant to glutamate-mediated cytotoxicity. BANF1 upregulation promoted glutamate-induced apoptosis of HT-22 cells by enhancing ROS generation.

Selective neuronal vulnerability to deficits in RNA processing

Emerging evidence indicates that errors in RNA processing can causally drive neurodegeneration. Given that RNA produced from expressed genes of all cell types undergoes processing (splicing, polyadenylation, 5' capping, etc.), the particular vulnerability of neurons to deficits in RNA processing calls for careful consideration. The activity-dependent transcriptome remodeling associated with synaptic plasticity in neurons requires rapid, multilevel post-transcriptional RNA processing events that provide additional opportunities for dysregulation and consequent introduction or persistence of errors in RNA transcripts. Here we review the accumulating evidence that neurons have an enhanced propensity for errors in RNA processing alongside grossly insufficient defenses to clear misprocessed RNA compared to other cell types. Additionally, we explore how tau, a microtubule-associated protein implicated in Alzheimer's disease and related tauopathies, contributes to deficits in RNA processing and clearance.

Identification of key lipid metabolism-related genes in Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) represents profound degenerative conditions of the brain that cause significant deterioration in memory and cognitive function. Despite extensive research on the significant contribution of lipid metabolism to AD progression, the precise mechanisms remain incompletely understood. Hence, this study aimed to identify key differentially expressed lipid metabolism-related genes (DELMRGs) in AD progression.

METHODS

Comprehensive analyses were performed to determine key DELMRGs in AD compared to controls in GSE122063 dataset from Gene Expression Omnibus. Additionally, the ssGSEA algorithm was utilized for estimating immune cell levels. Subsequently, correlations between key DELMRGs and each immune cell were calculated specifically in AD samples. The key DELMRGs expression levels were validated via two external datasets. Furthermore, gene set enrichment analysis (GSEA) was utilized for deriving associated pathways of key DELMRGs. Additionally, miRNA-TF regulatory networks of the key DELMRGs were constructed using the miRDB, NetworkAnalyst 3.0, and Cytoscape software. Finally, based on key DELMRGs, AD samples were further segmented into two subclusters via consensus clustering, and immune cell patterns and pathway differences between the two subclusters were examined.

RESULTS

Seventy up-regulated and 100 down-regulated DELMRGs were identified. Subsequently, three key DELMRGs (DLD, PLPP2, and PLAAT4) were determined utilizing three algorithms [(i) LASSO, (ii) SVM-RFE, and (iii) random forest]. Specifically, PLPP2 and PLAAT4 were up-regulated, while DLD exhibited downregulation in AD cerebral cortex tissue. This was validated in two separate external datasets (GSE132903 and GSE33000). The AD group exhibited significantly altered immune cell composition compared to controls. In addition, GSEA identified various pathways commonly associated with three key DELMRGs. Moreover, the regulatory network of miRNA-TF for key DELMRGs was established. Finally, significant differences in immune cell levels and several pathways were identified between the two subclusters.

CONCLUSION

This study identified DLD, PLPP2, and PLAAT4 as key DELMRGs in AD progression, providing novel insights for AD prevention/treatment.

A Continuous Extension of Gene Set Enrichment Analysis using the Likelihood Ratio Test Statistics Identifies VEGF as a Candidate Pathway for Alzheimer's disease

Background

Alzheimer's disease involves brain pathologies such as amyloid plaque depositions and hyperphosphorylated tau tangles and is accompanied by cognitive decline. Identifying the biological mechanisms underlying disease onset and progression based on quantifiable phenotypes will help understand the disease etiology and devise therapies.

Objective

Our objective was to identify molecular pathways associated with AD biomarkers (Amyloid-β and tau) and cognitive status (MMSE) accounting for variables such as age, sex, education, and APOE genotype.

Methods

We introduce a novel pathway-based statistical approach, extending the gene set likelihood ratio test to continuous phenotypes. We first analyzed independently each of the three phenotypes (Amyloid-β, tau, cognition), using continuous gene set likelihood ratio tests to account for covariates, including age, sex, education, and APOE genotype. The analysis involved a large sample size with data available for all three phenotypes, allowing for the identification of common pathways.

Results

We identified 14 pathways significantly associated with Amyloid-β, 5 associated with tau, and 174 associated with MMSE. Surprisingly, the MMSE outcome showed a larger number of significant pathways compared to biomarkers. A single pathway, vascular endothelial growth factor receptor binding (VEGF-RB), exhibited significant associations with all three phenotypes.

Conclusions

The study's findings highlight the importance of the VEGF signaling pathway in aging in AD. The complex interactions within the VEGF signaling family offer valuable insights for future therapeutic interventions.

Single cell characteristics of patients with vaccine-related adverse reactions following inactivated COVID-19 vaccination

A good safety and immunogenicity profile was reported in Phase I and II clinical trials of inactivated SARS-CoV-2 vaccines. Here, we report two cases associated with vaccine-associated adverse events, including one patient with fever and another with anaphylactic shock resulting from inactivated SARS-CoV-2 vaccination. Cell sub-types and the importance of genetic characteristics were assessed using single-cell mRNA sequencing and machine learning. Overall, the patient with fever showed a significant increase in the numbers of cytotoxic CD8 T cells and MKI67high CD8 T cells. A potential concurrent infection with the Epstein-Barr virus enhanced interferon type I responses to vaccination against the virus. STAT1, E2F1, YBX1, and E2F7 played a key role in the transcription regulation of MKI67high CD8 T cells. In contrast, the patient with allergic shock displayed predominant increases in the numbers of S100A9high monocytes, activated CD4 T cells, and PPBPhigh megakaryocytes. The decision tree showed that LYZ and S100A8 in S100A9high monocytes contributed to the degranulation of neutrophils and activation of neutrophils involved in allergic shock. PPBP and PF4 were major contributors to platelet degranulation. These findings highlight the diversity of adverse reactions following inactivated SARS-CoV-2 vaccination and show the emerging role of cellular subtypes and central genes in vaccine-associated adverse reactions.

Transcriptome analysis reveals the neuroprotective effect of Dlg4 against fastigial nucleus stimulation-induced ischemia/reperfusion injury in rats

BACKGROUND

Previous studies have demonstrated that electrical stimulation of the cerebellar fastigial nucleus (FNS) can considerably decrease infarction volume and improve neurofunction restoration following cerebral ischemia. Nevertheless, the molecular mechanism of the neuroprotective effect of FNS is still vague.

METHODS

In this study, we developed a rat model of ischemia/reperfusion that included 1 h FNS followed by reperfusion for 3, 6, 12, 24, and 72 h. The expression profile of molecular alterations in brain tissues was obtained by transcriptome sequencing at five different time points. The function and pathway of miRNA expression pattern and core genes were annotated by Allen Brain Atlas, STRING database and Cytoscape software, so as to explore the mechanism of FNS-mediated neuroprotection.

RESULTS

The results indicated that FNS is associated with the neurotransmitter cycle pathway. FNS may regulate the release of monoamine neurotransmitters in synaptic vesicles by targeting the corresponding miRNAs through core Dlg4 gene, stimulate the Alternative polyadenylation (APA) incident's anti -apoptosis effect on the brain, and stimulate the interaction activation of neurons in cerebellum, cortex/thalamus and other brain regions, regulate neurovascular coupling, and reduce cerebral damage.

CONCLUSION

FNS may activate neuronal and neurovascular coupling by regulating the release of neurotransmitters in synaptic vesicles through the methylation of core Dlg4 gene and the corresponding transcription factors and protein kinases, inducing the anti-apoptotic mechanism of APA events. The findings from our investigation offer a new perspective on the way brain tissue responds to FNS-driven neuroprotection.

Ribosomal Dysfunction Is a Common Pathomechanism in Different Forms of Trichothiodystrophy

Mutations in a broad variety of genes can provoke the severe childhood disorder trichothiodystrophy (TTD) that is classified as a DNA repair disease or a transcription syndrome of RNA polymerase II. In an attempt to identify the common underlying pathomechanism of TTD we performed a knockout/knockdown of the two unrelated TTD factors TTDN1 and RNF113A and investigated the consequences on ribosomal biogenesis and performance. Interestingly, interference with these TTD factors created a nearly uniform impact on RNA polymerase I transcription with downregulation of UBF, disturbed rRNA processing and reduction of the backbone of the small ribosomal subunit rRNA 18S. This was accompanied by a reduced quality of decoding in protein translation and the accumulation of misfolded and carbonylated proteins, indicating a loss of protein homeostasis (proteostasis). As the loss of proteostasis by the ribosome has been identified in the other forms of TTD, here we postulate that ribosomal dysfunction is a common underlying pathomechanism of TTD.

Epigenetic silencing of OR and TAS2R genes expression in human orbitofrontal cortex at early stages of sporadic Alzheimer's disease

Modulation of brain olfactory (OR) and taste receptor (TASR) expression was recently reported in neurological diseases. However, there is still limited evidence of these genes' expression in the human brain and the transcriptional regulation mechanisms involved remain elusive. We explored the possible expression and regulation of selected OR and TASR in the human orbitofrontal cortex (OFC) of sporadic Alzheimer's disease (AD) and non-demented control specimens using quantitative real-time RT-PCR and ELISA. Global H3K9me3 amounts were measured on OFC total histone extracts, and H3K9me3 binding at each chemoreceptor locus was examined through native chromatin immunoprecipitation. To investigate the potential interactome of the repressive histone mark H3K9me3 in OFC specimens, native nuclear complex co-immunoprecipitation (Co-IP) was combined with reverse phase-liquid chromatography coupled to mass spectrometry analysis. Interaction between H3K9me3 and MeCP2 was validated by reciprocal Co-IP, and global MeCP2 levels were quantitated. We found that OR and TAS2R genes are expressed and markedly downregulated in OFC at early stages of sporadic AD, preceding the progressive reduction in their protein levels and the appearance of AD-associated neuropathology. The expression pattern did not follow disease progression suggesting transcriptional regulation through epigenetic mechanisms. We discovered an increase of OFC global H3K9me3 levels and a substantial enrichment of this repressive signature at ORs and TAS2Rs proximal promoter at early stages of AD, ultimately lost at advanced stages. We revealed the interaction between H3K9me3 and MeCP2 at early stages and found that MeCP2 protein is increased in sporadic AD. Findings suggest MeCP2 might be implicated in OR and TAS2R transcriptional regulation through interaction with H3K9me3, and as an early event, it may uncover a novel etiopathogenetic mechanism of sporadic AD.

Blood RNA transcripts reveal similar and differential alterations in fundamental cellular processes in Alzheimer's disease and other neurodegenerative diseases

BACKGROUND

Dysfunctional processes in Alzheimer's disease and other neurodegenerative diseases lead to neural degeneration in the central and peripheral nervous system. Research demonstrates that neurodegeneration of any kind is a systemic disease that may even begin outside of the region vulnerable to the disease. Neurodegenerative diseases are defined by the vulnerabilities and pathology occurring in the regions affected.

METHOD

A random forest machine learning analysis on whole blood transcriptomes from six neurodegenerative diseases generated unbiased disease-classifying RNA transcripts subsequently subjected to pathway analysis.

RESULTS

We report that transcripts of the blood transcriptome selected for each of the neurodegenerative diseases represent fundamental biological cell processes including transcription regulation, degranulation, immune response, protein synthesis, apoptosis, cytoskeletal components, ubiquitylation/proteasome, and mitochondrial complexes that are also affected in the brain and reveal common themes across six neurodegenerative diseases.

CONCLUSION

Neurodegenerative diseases share common dysfunctions in fundamental cellular processes. Identifying regional vulnerabilities will reveal unique disease mechanisms.

HIGHLIGHTS

Transcriptomics offer information about dysfunctional processes. Comparing multiple diseases will expose unique malfunctions within diseases. Blood RNA can be used ante mortem to track expression changes in neurodegenerative diseases. Protocol standardization will make public datasets compatible.

Atrophic astrocytes in aged marmosets present tau hyperphosphorylation, RNA oxidation, and DNA fragmentation

Astrocytes perform multiple essential functions in the brain showing morphological changes. Hypertrophic astrocytes are commonly observed in cognitively healthy aged animals, implying a functional defense mechanism without losing neuronal support. In neurodegenerative diseases, astrocytes show morphological alterations, such as decreased process length and reduced number of branch points, known as astroglial atrophy, with detrimental effects on neuronal cells. The common marmoset (Callithrix jacchus) is a non-human primate that, with age, develops several features that resemble neurodegeneration. In this study, we characterize the morphological alterations in astrocytes of adolescent (mean 1.75 y), adult (mean 5.33 y), old (mean 11.25 y), and aged (mean 16.83 y) male marmosets. We observed a significantly reduced arborization in astrocytes of aged marmosets compared to younger animals in the hippocampus and entorhinal cortex. These astrocytes also show oxidative damage to RNA and increased nuclear plaques in the cortex and tau hyperphosphorylation (AT100). Astrocytes lacking S100A10 protein show a more severe atrophy and DNA fragmentation. Our results demonstrate the presence of atrophic astrocytes in the brains of aged marmosets.

Distinct CSF biomarker-associated DNA methylation in Alzheimer's disease and cognitively normal subjects

BACKGROUND

Growing evidence has demonstrated that DNA methylation (DNAm) plays an important role in Alzheimer's disease (AD) and that DNAm differences can be detected in the blood of AD subjects. Most studies have correlated blood DNAm with the clinical diagnosis of AD in living individuals. However, as the pathophysiological process of AD can begin many years before the onset of clinical symptoms, there is often disagreement between neuropathology in the brain and clinical phenotypes. Therefore, blood DNAm associated with AD neuropathology, rather than with clinical data, would provide more relevant information on AD pathogenesis.

METHODS

We performed a comprehensive analysis to identify blood DNAm associated with cerebrospinal fluid (CSF) pathological biomarkers for AD. Our study included matched samples of whole blood DNA methylation, CSF Aβ42, phosphorylated tau181 (pTau181), and total tau (tTau) biomarkers data, measured on the same subjects and at the same clinical visits from a total of 202 subjects (123 CN or cognitively normal, 79 AD) in the Alzheimer's Disease Neuroimaging Initiative (ADNI) cohort. To validate our findings, we also examined the association between premortem blood DNAm and postmortem brain neuropathology measured on a group of 69 subjects in the London dataset.

RESULTS

We identified a number of novel associations between blood DNAm and CSF biomarkers, demonstrating that changes in pathological processes in the CSF are reflected in the blood epigenome. Overall, the CSF biomarker-associated DNAm is relatively distinct in CN and AD subjects, highlighting the importance of analyzing omics data measured on cognitively normal subjects (which includes preclinical AD subjects) to identify diagnostic biomarkers, and considering disease stages in the development and testing of AD treatment strategies. Moreover, our analysis revealed biological processes associated with early brain impairment relevant to AD are marked by DNAm in the blood, and blood DNAm at several CpGs in the DMR on HOXA5 gene are associated with pTau181 in the CSF, as well as tau-pathology and DNAm in the brain, nominating DNAm at this locus as a promising candidate AD biomarker.

CONCLUSIONS

Our study provides a valuable resource for future mechanistic and biomarker studies of DNAm in AD.

GTP energy dependence of endocytosis and autophagy in the aging brain and Alzheimer's disease

Increased interest in the aging and Alzheimer's disease (AD)-related impairments in autophagy in the brain raise important questions about regulation and treatment. Since many steps in endocytosis and autophagy depend on GTPases, new measures of cellular GTP levels are needed to evaluate energy regulation in aging and AD. The recent development of ratiometric GTP sensors (GEVALS) and findings that GTP levels are not homogenous inside cells raise new issues of regulation of GTPases by the local availability of GTP. In this review, we highlight the metabolism of GTP in relation to the Rab GTPases involved in formation of early endosomes, late endosomes, and lysosomal transport to execute the autophagic degradation of damaged cargo. Specific GTPases control macroautophagy (mitophagy), microautophagy, and chaperone-mediated autophagy (CMA). By inference, local GTP levels would control autophagy, if not in excess. Additional levels of control are imposed by the redox state of the cell, including thioredoxin involvement. Throughout this review, we emphasize the age-related changes that could contribute to deficits in GTP and AD. We conclude with prospects for boosting GTP levels and reversing age-related oxidative redox shift to restore autophagy. Therefore, GTP levels could regulate the numerous GTPases involved in endocytosis, autophagy, and vesicular trafficking. In aging, metabolic adaptation to a sedentary lifestyle could impair mitochondrial function generating less GTP and redox energy for healthy management of amyloid and tau proteostasis, synaptic function, and inflammation.

Intermittent treatment with Apremilast, a phosphodiesterase-4 inhibitor, ameliorates Alzheimer's-like pathology and symptoms through multiple targeting actions in aged T2D rats

BACKGROUND

Apremilast (Apre), a novel phosphodiesterase-4 (PDE4) inhibitor, has been shown to have anti-inflammatory, immunomodulator, neuroprotective and senolytic properties, therefore, Apre like other PDE4 inhibitors may be a promising candidate for treatment of Alzheimer's disease (AD).

OBJECTIVE

To evaluate the effectiveness of Apre on Alzheimer's like pathology and symptoms in an animal model.

METHODS

The effects of Apre and cilostazol, a reference drug, on the behavioral, biochemical, and pathological features of Alzheimer's disease induced by a high-fat/high-fructose diet combined with low-dose streptozotocin (HF/HFr/l-STZ) were investigated.

RESULT

Apre 5 mg/kg IP/day for 3 consecutive days per week for 8 weeks attenuated memory and learning deficits tested by novel object recognition, Morris water maze and passive avoidance tests. Apre treatment significantly decreased the number of degenerating cells, and abnormal suppression of gene expression of AMPA and NMDA receptor subunits in the cortex and hippocampus of the AD rat model compared to rats that received vehicle. A significant decrease in elevated levels of hippocampal amyloid beta, tau-positive cell count, cholinesterase activity, and hippocampal caspase-3, a biomarker of neurodegeneration, was also observed after treatment with Apre in AD rats compared to rats that received placebo. Furthermore, a significant decrease in pro-inflammatory cytokines, oxidative stress, insulin resistance and GSK-3 was demonstrated in AD aged rats treated by Apre.

CONCLUSION

Our findings demonstrate that intermittent treatment with Apre can enhance cognitive function in HF/HFr/l-STZ rats which may be related to decreased pro-inflammatory cytokines, oxidative stress, insulin resistance and GSK-3β.

Distinct CSF biomarker-associated DNA methylation in Alzheimer's disease and cognitively normal subjects

Background Growing evidence has demonstrated that DNA methylation (DNAm) plays an important role in Alzheimer's disease (AD) and that DNAm differences can be detected in the blood of AD subjects. Most studies have correlated blood DNAm with the clinical diagnosis of AD in living individuals. However, as the pathophysiological process of AD can begin many years before the onset of clinical symptoms, there is often disagreement between neuropathology in the brain and clinical phenotypes. Therefore, blood DNAm associated with AD neuropathology, rather than with clinical data, would provide more relevant information on AD pathogenesis. Methods We performed a comprehensive analysis to identify blood DNAm associated with cerebrospinal fluid (CSF) pathological biomarkers for AD. Our study included matched samples of whole blood DNA methylation, CSF Aβ 42 , phosphorylated tau 181 (pTau 181 ), and total tau (tTau) biomarkers data, measured on the same subjects and at the same clinical visits from a total of 202 subjects (123 CN or cognitively normal, 79 AD) in the Alzheimer's Disease Neuroimaging Initiative (ADNI) cohort. To validate our findings, we also examined the association between premortem blood DNAm and postmortem brain neuropathology measured on a group of 69 subjects in the London dataset. Results We identified a number of novel associations between blood DNAm and CSF biomarkers, demonstrating that changes in pathological processes in the CSF are reflected in the blood epigenome. Overall, the CSF biomarker-associated DNAm is relatively distinct in CN and AD subjects, highlighting the importance of analyzing omics data measured on cognitively normal subjects (which includes preclinical AD subjects) to identify diagnostic biomarkers, and considering disease stages in the development and testing of AD treatment strategies. Moreover, our analysis revealed biological processes associated with early brain impairment relevant to AD are marked by DNAm in the blood, and blood DNAm at several CpGs in the DMR on HOXA5 gene are associated with pTau 181 in the CSF, as well as tau-pathology and DNAm in the brain, nominating DNAm at this locus as a promising candidate AD biomarker. Conclusions Our study provides a valuable resource for future mechanistic and biomarker studies of DNAm in AD.

Proteomic alterations in the cerebellum and hippocampus in an Alzheimer's disease mouse model: Alleviating effect of palmatine

Alzheimer's disease (AD) is one of the most prevalent diseases that lead to memory deficiencies, severe behavioral abnormalities, and ultimately death. The need for more appropriate treatment of AD continues, and remains a sought-after goal. Previous studies showed palmatine (PAL), an isoquinoline alkaloid, might have the potential for combating AD because of its in vitro and in vivo activities. In this study, we aimed to assess PAL's therapeutic potential and gain insights into the working mechanism on protein level in the AD mouse model brain, for the first time. To this end, PAL was administered to 12-month-old 5xFAD mice at two doses after its successful isolation from the Siberian barberry shrub. PAL (10 mg/kg) showed statistically significant improvement in the memory and learning phase on the Morris water maze test. The PAL's ability to pass through the blood-brain barrier was verified via Multiple Reaction Monitoring (MRM). Label-free proteomics analysis revealed PAL administration led to changes most prominently in the cerebellum, followed by the hippocampus, but none in the cortex. Most of the differentially expressed proteins in PAL compared to the 5xFAD control group (ALZ) were the opposite of those in ALZ in comparison to healthy Alzheimer's littermates (ALM) group. HS105, HS12A, and RL12 were detected as hub proteins in the cerebellum. Collectively, here we present PAL as a potential therapeutic candidate owing to its alleviating effect in 5xFAD mice on not only cognitive impairment but also proteomes in the cerebellum and hippocampus.

Ribosome biogenesis in disease: new players and therapeutic targets

The ribosome is a multi-unit complex that translates mRNA into protein. Ribosome biogenesis is the process that generates ribosomes and plays an essential role in cell proliferation, differentiation, apoptosis, development, and transformation. The mTORC1, Myc, and noncoding RNA signaling pathways are the primary mediators that work jointly with RNA polymerases and ribosome proteins to control ribosome biogenesis and protein synthesis. Activation of mTORC1 is required for normal fetal growth and development and tissue regeneration after birth. Myc is implicated in cancer development by enhancing RNA Pol II activity, leading to uncontrolled cancer cell growth. The deregulation of noncoding RNAs such as microRNAs, long noncoding RNAs, and circular RNAs is involved in developing blood, neurodegenerative diseases, and atherosclerosis. We review the similarities and differences between eukaryotic and bacterial ribosomes and the molecular mechanism of ribosome-targeting antibiotics and bacterial resistance. We also review the most recent findings of ribosome dysfunction in COVID-19 and other conditions and discuss the consequences of ribosome frameshifting, ribosome-stalling, and ribosome-collision. We summarize the role of ribosome biogenesis in the development of various diseases. Furthermore, we review the current clinical trials, prospective vaccines for COVID-19, and therapies targeting ribosome biogenesis in cancer, cardiovascular disease, aging, and neurodegenerative disease.

CRISPRi screening reveals regulators of tau pathology shared between exosomal and vesicle-free tau

The aggregation of the microtubule-associated protein tau is a defining feature of Alzheimer's disease and other tauopathies. Tau pathology is believed to be driven by free tau aggregates and tau carried within exosome-like extracellular vesicles, both of which propagate trans-synaptically and induce tau pathology in recipient neurons by a corrupting process of seeding. Here, we performed a genome-wide CRISPRi screen in tau biosensor cells and identified cellular regulators shared by both mechanisms of tau seeding. We identified ANKLE2, BANF1, NUSAP1, EIF1AD, and VPS18 as the top validated regulators that restrict tau aggregation initiated by both exosomal and vesicle-free tau seeds. None of our validated hits affected the uptake of either form of tau seeds, supporting the notion that they operate through a cell-autonomous mechanism downstream of the seed uptake. Lastly, validation studies with human brain tissue also revealed that several of the identified protein hits are down-regulated in the brains of Alzheimer's patients, suggesting that their decreased activity may be required for the emergence or progression of tau pathology in the human brain.

The Caribbean-Hispanic Alzheimer's disease brain transcriptome reveals ancestry-specific disease mechanisms

Identifying ancestry-specific molecular profiles of late-onset Alzheimer's Disease (LOAD) in brain tissue is crucial to understand novel mechanisms and develop effective interventions in non-European, high-risk populations. We performed gene differential expression (DE) and consensus network-based analyses in RNA-sequencing data of postmortem brain tissue from 39 Caribbean Hispanics (CH). To identify ancestry-concordant and -discordant expression profiles, we compared our results to those from two independent non-Hispanic White (NHW) samples (n = 731). In CH, we identified 2802 significant DE genes, including several LOAD known-loci. DE effects were highly concordant across ethnicities, with 373 genes transcriptome-wide significant in all three cohorts. Cross-ancestry meta-analysis found NPNT to be the top DE gene. We replicated over 82% of meta-analyses genome-wide signals in single-nucleus RNA-seq data (including NPNT and LOAD known-genes SORL1, FBXL7, CLU, ABCA7). Increasing representation in genetic studies will allow for deeper understanding of ancestry-specific mechanisms and improving precision treatment options in understudied groups.

Role of primary aging hallmarks in Alzheimer´s disease

Alzheimer's disease (AD) is the most common neurodegenerative disease, which severely threatens the health of the elderly and causes significant economic and social burdens. The causes of AD are complex and include heritable but mostly aging-related factors. The primary aging hallmarks include genomic instability, telomere wear, epigenetic changes, and loss of protein stability, which play a dominant role in the aging process. Although AD is closely associated with the aging process, the underlying mechanisms involved in AD pathogenesis have not been well characterized. This review summarizes the available literature about primary aging hallmarks and their roles in AD pathogenesis. By analyzing published literature, we attempted to uncover the possible mechanisms of aberrant epigenetic markers with related enzymes, transcription factors, and loss of proteostasis in AD. In particular, the importance of oxidative stress-induced DNA methylation and DNA methylation-directed histone modifications and proteostasis are highlighted. A molecular network of gene regulatory elements that undergoes a dynamic change with age may underlie age-dependent AD pathogenesis, and can be used as a new drug target to treat AD.

In-Depth Proteomic Analysis of De Novo Proteome in a Mouse Model of Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is the most common dementia syndrome in the elderly characterized by synaptic failure and unique brain pathology. De novo protein synthesis is required for the maintenance of memory and synaptic plasticity. Mounting evidence links impaired neuronal protein synthesis capacity and overall protein synthesis deficits to AD pathogenesis. Meanwhile, identities of AD-associated dysregulation of "newly synthesized proteome" remain elusive.

OBJECTIVE

To investigate de novo proteome alterations in the hippocampus of aged Tg19959 AD model mice.

METHODS

In this study, we combined the bioorthogonal noncanonical amino acid tagging (BONCAT) method with the unbiased large-scale proteomic analysis in acute living brain slices (we name it "BONSPEC") to investigate de novo proteome alterations in the hippocampus of Tg19959 AD model mice. We further applied multiple bioinformatics methods to analyze in-depth the proteomics data.

RESULTS

In total, 1,742 proteins were detected across the 10 samples with the BONSPEC method. After exclusion of those only detected in less than half of the samples in both groups, 1,362 proteins were kept for further analysis. 37 proteins were differentially expressed (based on statistical analysis) between the WT and Tg19959 groups. Among them, 19 proteins were significantly decreased while 18 proteins were significantly increased in the hippocampi of Tg19959 mice compared to WT mice. The results suggest that proteins involved in synaptic function were enriched in de novo proteome of AD mice.

CONCLUSION

Our study could provide insights into the future investigation into the molecular signaling mechanisms underlying AD and related dementias (ADRDs).

HP1 proteins regulate nucleolar structure and function by secluding pericentromeric constitutive heterochromatin

Nucleoli are nuclear compartments regulating ribosome biogenesis and cell growth. In embryonic stem cells (ESCs), nucleoli containing transcriptionally active ribosomal genes are spatially separated from pericentromeric satellite repeat sequences packaged in largely repressed constitutive heterochromatin (PCH). To date, mechanisms underlying such nuclear partitioning and the physiological relevance thereof are unknown. Here we show that repressive chromatin at PCH ensures structural integrity and function of nucleoli during cell cycle progression. Loss of heterochromatin proteins HP1α and HP1β causes deformation of PCH, with reduced H3K9 trimethylation (H3K9me3) and HP1γ levels, absence of H4K20me3 and upregulated major satellites expression. Spatially, derepressed PCH aberrantly associates with nucleoli accumulating severe morphological defects during S/G2 cell cycle progression. Hp1α/β deficiency reduces cell proliferation, ribosomal RNA biosynthesis and mobility of Nucleophosmin, a major nucleolar component. Nucleolar integrity and function require HP1α/β proteins to be recruited to H3K9me3-marked PCH and their ability to dimerize. Correspondingly, ESCs deficient for both Suv39h1/2 H3K9 HMTs display similar nucleolar defects. In contrast, Suv4-20h1/2 mutant ESCs lacking H4K20me3 at PCH do not. Suv39h1/2 and Hp1α/β deficiency-induced nucleolar defects are reminiscent of those defining human ribosomopathy disorders. Our results reveal a novel role for SUV39H/HP1-marked repressive constitutive heterochromatin in regulating integrity, function and physiology of nucleoli.

Pathological Nuclear Hallmarks in Dentate Granule Cells of Alzheimer’s Patients: A Biphasic Regulation of Neurogenesis

The dentate gyrus (DG) of the human hippocampus is a complex and dynamic structure harboring mature and immature granular neurons in diverse proliferative states. While most mammals show persistent neurogenesis through adulthood, human neurogenesis is still under debate. We found nuclear alterations in granular cells in autopsied human brains, detected by immunohistochemistry. These alterations differ from those reported in pyramidal neurons of the hippocampal circuit. Aging and early AD chromatin were clearly differentiated by the increased epigenetic markers H3K9me3 (heterochromatin suppressive mark) and H3K4me3 (transcriptional euchromatin mark). At early AD stages, lamin B2 was redistributed to the nucleoplasm, indicating cell-cycle reactivation, probably induced by hippocampal nuclear pathology. At intermediate and late AD stages, higher lamin B2 immunopositivity in the perinucleus suggests fewer immature neurons, less neurogenesis, and fewer adaptation resources to environmental factors. In addition, senile samples showed increased nuclear Tau interacting with aged chromatin, likely favoring DNA repair and maintaining genomic stability. However, at late AD stages, the progressive disappearance of phosphorylated Tau forms in the nucleus, increased chromatin disorganization, and increased nuclear autophagy support a model of biphasic neurogenesis in AD. Therefore, designing therapies to alleviate the neuronal nuclear pathology might be the only pathway to a true rejuvenation of brain circuits.

Epigenetic Changes and Chromatin Reorganization in Brain Function: Lessons from Fear Memory Ensemble and Alzheimer’s Disease

Healthy brain functioning in mammals requires a continuous fine-tuning of gene expression. Accumulating evidence over the last three decades demonstrates that epigenetic mechanisms and dynamic changes in chromatin organization are critical components during the control of gene transcription in neural cells. Recent genome-wide analyses show that the regulation of brain genes requires the contribution of both promoter and long-distance enhancer elements, which must functionally interact with upregulated gene expression in response to physiological cues. Hence, a deep comprehension of the mechanisms mediating these enhancer–promoter interactions (EPIs) is critical if we are to understand the processes associated with learning, memory and recall. Moreover, the onset and progression of several neurodegenerative diseases and neurological alterations are found to be strongly associated with changes in the components that support and/or modulate the dynamics of these EPIs. Here, we overview relevant discoveries in the field supporting the role of the chromatin organization and of specific epigenetic mechanisms during the control of gene transcription in neural cells from healthy mice subjected to the fear conditioning paradigm, a relevant model to study memory ensemble. Additionally, special consideration is dedicated to revising recent results generated by investigators working with animal models and human postmortem brain tissue to address how changes in the epigenome and chromatin architecture contribute to transcriptional dysregulation in Alzheimer’s disease, a widely studied neurodegenerative disease. We also discuss recent developments of potential new therapeutic strategies involving epigenetic editing and small chromatin-modifying molecules (or epidrugs).

Cognitive Decline and BPSD Are Concomitant with Autophagic and Synaptic Deficits Associated with G9a Alterations in Aged SAMP8 Mice

Behavioural and psychological symptoms of dementia (BPSD) are presented in 95% of Alzheimer’s Disease (AD) patients and are also associated with neurotrophin deficits. The molecular mechanisms leading to age-related diseases are still unclear; however, emerging evidence has suggested that epigenetic modulation is a key pathophysiological basis of ageing and neurodegeneration. In particular, it has been suggested that G9a methyltransferase and its repressive histone mark (H3K9me2) are important in shaping learning and memory by modulating autophagic activity and synaptic plasticity. This work deepens our understanding of the epigenetic mechanisms underlying the loss of cognitive function and BPSD in AD. For this purpose, several tasks were performed to evaluate the parameters of sociability (three-chamber test), aggressiveness (resident intruder), anxiety (elevated plus maze and open field) and memory (novel object recognition test) in mice, followed by the evaluation of epigenetic, autophagy and synaptic plasticity markers at the molecular level. The behavioural alterations presented by senescence-accelerated mice prone 8 (SAMP8) of 12 months of age compared with their senescence-accelerated mouse resistant mice (SAMR1), the healthy control strain was accompanied by age-related cognitive deficits and alterations in epigenetic markers. Increased levels of G9a are concomitant to the dysregulation of the JNK pathway in aged SAMP8, driving a failure in autophagosome formation. Furthermore, lower expression of the genes involved in the memory-consolidation process modulated by ERK was observed in the aged male SAMP8 model, suggesting the implication of G9a. In any case, two of the most important neurotrophins, namely brain-derived neurotrophic factor (Bdnf) and neurotrophin-3 (NT3), were found to be reduced, along with a decrease in the levels of dendritic branching and spine density presented by SAMP8 mice. Thus, the present study characterizes and provides information regarding the non-cognitive and cognitive states, as well as molecular alterations, in aged SAMP8, demonstrating the AD-like symptoms presented by this model. In any case, our results indicate that higher levels of G9a are associated with autophagic deficits and alterations in synaptic plasticity, which could further explain the BPSD and cognitive decline exhibited by the model.

Cross-tissue analysis of blood and brain epigenome-wide association studies in Alzheimer's disease

To better understand DNA methylation in Alzheimer's disease (AD) from both mechanistic and biomarker perspectives, we performed an epigenome-wide meta-analysis of blood DNA methylation in two large independent blood-based studies in AD, the ADNI and AIBL studies, and identified 5 CpGs, mapped to the SPIDR, CDH6 genes, and intergenic regions, that are significantly associated with AD diagnosis. A cross-tissue analysis that combined these blood DNA methylation datasets with four brain methylation datasets prioritized 97 CpGs and 10 genomic regions that are significantly associated with both AD neuropathology and AD diagnosis. An out-of-sample validation using the AddNeuroMed dataset showed the best performing logistic regression model includes age, sex, immune cell type proportions, and methylation risk score based on prioritized CpGs in cross-tissue analysis (AUC = 0.696, 95% CI: 0.616 - 0.770, P-value = 2.78 × 10^-5). Our study offers new insights into epigenetics in AD and provides a valuable resource for future AD biomarker discovery.

Neuronal nuclear tau and neurodegeneration

Tau is a well-known microtubule-associated protein related to its cytoplasmic localization in a neuronal cell. However, tau has been located at the cell nucleus where it could be a nucleic acid-associated protein by its preferential binding to DNA sequences present in the nucleolus and pericentromeric heterochromatin. This less well-known localization of tau could not be trivial, since during aging, an increase in the amount of nuclear tau takes place and it may be related to the described role of tau in the activation of transposons and further aging acceleration.